The present invention relates to an image forming apparatus for use in a digital copier, a printer, or similar apparatus, which records data for each pixel.
There is a case, as indicated in FIG. 6, in which a digital copier or a similar apparatus, using, for example, laser beams, comprises a scanner 300, an image processing section 400, and a printer section 100 (See, for example, Japanese Patent Publication Open to Public Inspection No. 157070/1987). The scanner section 300 optically scans a document 200 and converts its image information into an optical image. The optical image is supplied to the image processing section 400, converted into an image signal, and the image signal is image processed in a predetermined manner. Image processing includes enlargement and/or reduction processing, half-toning, outline-processing, and in the case of color composition, color ghost processing, etc. In the printer section 100, an image is recorded according to a digital image signal (pixel data), having a predetermined number of bits, which has been formed in the image processing section 400. When an example of the printer section 100 is shown, an electrophotographic type printer using a photoreceptor drum is used, and laser beams are used as a light source to form an electrostatic latent image on the photoreceptor drum.
In such a digital copier, an increase of copying speed by reduction of image processing time is required. Further, in an apparatus which can be switched between 400 DPI processing and 600 DPI processing, in the case where the image processing section corresponds to, for example, 400 DPI processing, the number of pixels in the scanning line is increased by 1.5 times in the primary scanning direction for 600 DPI processing, and is increased by 2.25 times in the combination of the primary and subsidiary scanning direction. Therefore, it takes much more processing time than does 400 DPI processing, and the copying speed is consequently decreased.